I was so dead-set on being highly successful at a young age, that my default answer was “yes.” I was so bad, sometimes I’d agree to doing something before even knowing what the task was, or volunteer myself for assignments I wasn’t the most qualified for – all in an attempt to prove myself. That’s not exactly the best way to get ahead.

While I’ve since learned the hard way that saying no can be for the best, it’s not an easy thing to learn. Are you a people pleaser? Do you consider yourself the type of person who says yes to everything?

It’s incredibly normal to feel uncomfortable saying “no” to a boss, supervisor or client, but there are ways to turn someone down while still maintaining a healthy and respectful relationship. The secret lies largely in giving positive, constructive reasons for responding in the negative.

When to reject

What I didn’t know earlier in my career was that it’s entirely possible to say no in a way that builds a relationship rather than tearing it down. If you turn down an assignment, it’s important to thoroughly explain your reasons for doing so, and then offer an alternative.

If you present your argument in a diplomatic yet direct way, your boss/client/etc. will likely be less defensive, and more open to hearing what you have to say.

Greg McKeown illustrates this point perfectly in his terrific bestseller, “Essentialism.” When your boss asks you to tackle a new project, McKeown recommends asking which of your other assignments can be put to the side so that you will have enough time to devote to the new task.

The beauty of this strategy is that you’re getting your point across without actually saying no.

The idea of a positive no is, in many ways, to promote efficiency and excellence. For example, when holding a meeting, McKeown advises: “ask what is its one key purpose—the one thing you want to have happen as a result. If there isn’t one, then don’t have the meeting. And if there is, then fight for that one thing in the meeting. And when you have got it, end the meeting.”

Whether it’s at work or at home, there are consequences to taking on more than you can handle. The more we try to juggle, the less focused and less productive we become overall.

For example, if my team is strapped focusing on work for our existing clients, and we get approached by a Fortune 500 brand needing our assistance in crafting a digital strategy, we have to seriously consider saying no to the new project. While we would love to participate in the project, we have to be prepared to say no if the end result won’t be to our exacting standards.

In some cases, it’s in your best interest to be accommodating. And if it’s a project you’re genuinely excited about, find out if the deadline is flexible—or if you can re-prioritize other work. But other times it makes more sense to politely decline.

The trick – and it’s not always easy – is learning to tell the difference

I’ve had younger professionals ask me when they can practice the art of saying no. It might be appropriate to say the dreaded word when:

There’s not enough time

Be realistic if there aren’t enough hours in the day—or week—to finish the assignment. If you’re not sure if you have enough time, try to estimate how long it will take to complete everything on your plate already.

When in doubt, add some cushion, as I’ve found nine out of ten projects take more time than you’d initially expect.

The rest of your work will suffer

Will taking on another project prevent you from giving other tasks the proper time and attention? Don’t put yourself in the position of missing a deadline or doing a rushed job.

If you botch a task you had previously agreed to, no one’s going to focus on that extra job you just said yes to – they’re going to focus on the one you flubbed.

You don’t feel qualified

If you don’t feel confident that you have the skills to do what’s being asked of you, it’s in your best interest to say so.

In this situation, your boss might reply , “I wouldn’t give this to you if I thought you couldn’t handle it.” It’s a flattering thing to say, but if you truly feel ill-prepared, support your original stance by making a list of resources you would need in order to feel comfortable taking on the project.

The company itself will suffer

At times, you’ll be asked to do something that you know will put the company in worse financial shape, even if your boss doesn’t yet realize it. It’s a difficult situation to be in, but you have to be prepared to suggest the counterpoint in a non-threatening way.

Be sure to have cold hard data at your fingertips, and anticipate any questions that might be asked. Let the other party reconsider their initial request; if you don’t come off as too strident in your argument, you might just win them over, and win some respect in the process.

My advice? Get good at saying no, when appropriate. It’s a wonderful skill to build over time. If you’re doing it right, it can not only improve your career trajectory, but help you get the respect you deserve, as well.